Update documentation for more next-error features

Update documentation for more next-error features

* doc/emacs/maintaining.texi (Change Log Commands): Mention
change-log-goto-source.

* doc/emacs/building.texi (Compilation Mode): Document
next-error-find-buffer-function and next-error-select-buffer.

* doc/emacs/building.texi (Grep Searching):
* doc/emacs/files.texi (Diff Mode):
* doc/emacs/search.texi (Other Repeating Search):
* doc/emacs/windows.texi (Displaying Buffers):
Prefer ‘M-g M-n’ over ‘C-x `’.

* lisp/simple.el (next-error-find-buffer-function, next-error)
(next-error-select-buffer): Elaborate docstrings.  (Bug#20493)